FIGS. 10 and 11 illustrate a conventional chip resistor. The chip resistor 1A shown in FIG. 10 is disclosed in JP-A-2002-57009, and the chip resistor 2A shown in FIG. 11 is disclosed in JP-A-2002-57010.
As shown in FIG. 10, the chip resistor 1A includes a metal resistor element 100 and a pair of copper electrodes 110. The electrodes 110 are fixed to a lower surface 100a of the resistor element 100 and spaced from each other in the direction X in the figure. Each of the electrodes 110 includes a lower surface provided with a solder layer 130.
The chip resistor 1A is surface-mounted on e.g. printed circuit board, using solder. It is desirable that melted solder uniformly contacts with the entire lower surface of each of the electrode 110. However, the melted solder may contact only with an inner surface 111 and its vicinity of the electrode 110. The melted solder may also contact with only an outer surface 112 of the electrode 110. The chip resistor 1A may provide different resistances in the former case and in the latter case. Thus, a circuit using the chip resistor 1A may not have a desirable electrical property depending on the soldering condition. Such disadvantage is noticeable especially in a chip resistor having a low resistance (not more than 100 mΩ for example).
The chip resistor 2A shown in FIG. 11 includes a pair of bonding pads 120 in addition to the features of the above-described chip resistor 1A. Specifically, the two bonding pads 120 are fixed to an upper surface 100b of the resistor element 100 and spaced from each other in the direction X. As shown, each of the bonding pads 120 is arranged right above a respective one of the electrodes 110. The bonding pad 120 is made of a material suitable for wire bonding such as nickel, and has a specific resistance lower than that of the resistor element 100.
In the chip resistor 2A with the above structure, the resistance is lower at each end portion (i.e. the aggregate portion consisting of an electrode 110, a bonding pad 120, and an end region of the resistor element 110 that is sandwiched by the former two components) than when the bonding pad 120 is not provided (see the chip resistor 1A shown in FIG. 10). Accordingly, the above-described disadvantage of the chip resistor 1A can be reduced or practically eliminated in the chip resistor 2A.
However, in the chip resistor 2A shown in FIG. 11, the electrodes 110 are made of copper, while the bonding pads 120 are made of nickel, for example. Thus, two different materials must be prepared for forming the electrodes and the bonding pads. Further, the electrodes 110 and the bonding pads 120, which are made of different materials, must be formed in different process steps. As a result, the product cost of the chip resistor 2A is disadvantageously increased.